The present invention relates to an internal combustion engine cooling system, and, more particularly, relates to an internal combustion engine cooling system which provides either combined cooling for a cylinder head and a cylinder block of the engine, or either partly or totally separated cooling for the cylinder head and the cylinder block, according to operational conditions.
There are various considerations which arise with regard to the cooling of internal combustion engines which are cooled by the circulation of cooling fluid in passages or cooling jackets formed in the cylinder head and in the cylinder block thereof. Some of these considerations relate to the cooling of the cylinder head, and others to the cooling of the cylinder block. Nowadays the prior art type old or conventional ways of cooling an internal combustion engine, in which the cooling fluid for the cylinder head was always completely mixed with that for the cylinder block, thus ensuring that the cylinder head and the cylinder block were always at substantially the same temperature, have become inadequate.
One of these considerations is that it is important to maximize the thermal efficiency of an internal combustion engine, and in order to do this it is effective to increase the compression ratio of the engine. However, increase of the compression ratio of the engine is limited by the occurrence of so called knocking or pinking, i.e. of detonation caused by compression ignition, not caused by any spark from a spark plug, of the air-fuel mixture within the combustion chambers of the engine. The occurrence of knocking is generally reduced by keeping the cylinder head as cool as possible, and accordingly when an internal combustion engine is being operated, especially in operational conditions in which the occurrence of knocking is a high possibility, such as high rotational speed high engine load operational conditions, it is very important to cool the cylinder head down to as low a temperature as possible, consistent with other operational considerations.
On the other hand, it is not very advantageous to cool down the cylinder block of the engine to a very low temperature, because in that case the temperature of the lubricating oil contained within the cylinder block, which is of course strongly influenced by the temperature of the cylinder block, becomes rather low, thus increasing the viscosity of this lubricating oil and causing unacceptably high mechanical energy losses in the engine. Further, because the viscosity of the lubricating oil within the cylinder block when this oil is cold, i.e. when it is not at proper operating temperature, is higher than when said lubricating oil is at operating temperature, therefore of course while this lubricating oil is cold this causes substantially increased use of fuel by the internal combustion engine, which is very wasteful. Further, if the temperature of the walls of the cylinders of the engine, i.e. the temperature of the bores thereof, becomes low, then the amount of uncombusted hydrocarbons in the exhaust gases emitted by the engine rises, which can cause a serious problem in view of the standards for control of pollution by automobiles, which are becoming more and more severe nowadays.
Another problem that occurs if the temperature of the cylinder block gets low is that wear on the various moving parts of the internal combustion engine, especially bore wear, rises dramatically. In fact, a large proportion of the wear on the bores of an internal combustion engine occurs when the engine is in the non fully warmed up condition, both because the lubricating qualities of the lubricating oil in the engine are not good at low temperatures, and also because the state of mechanical fit to which the parts of the engine are "worn in" or "run in" is appropriate to their physical dimensions when at proper engine operating temperature, and accordingly in the cold or the semi cold condition these parts do not mate together very well.
These problems that arise when the cylinder block of an internal combustion engine becomes too cold during actual running operation of the engine of course also apply with equal force during the warming up process of the internal combustion engine, after it has been started up from the cold condition and before it has attained normal operating temperature. Especially, the problem of excessive wear on the moving parts of the internal combustion engine, and the problem of excessive emission of uncombusted hydrocarbons in the exhaust gases of the internal combustion engine, are particularly serious during warming up operation. In fact, in view of this matter, it has in the past been an important design goal for internal combustion engines for the moving parts thereof to be warmed up as soon as practicable, or at any rate to be brought to an intermediate temperature higher than a very cold non operating temperature as soon as practicable.
According to these considerations, it is important to warm up the cylinder block of an internal combustion engine as quickly as possible, when the engine is started from the cold condition, and to keep the cylinder block at quite a high operating temperature thereafter. A difficulty arises in this regard, because during the operation of an internal combustion engine most of the heat which is being generated in the combustion chambers thereof by combustion of air-fuel mixture therein is in fact communicated not to the cylinder block of the engine, but to the cylinder head thereof. Therefore transfer of heat from the cylinder head wherein said heat is generated to the cylinder block is very important, especially during the warming up process of the engine. Of course, such heat transfer can take place by the process of heat conduction, since the cylinder head is clamped to the cylinder block, typically however with the interposition between of a head gasket which may have a rather low heat conductivity. However, it is desirable to convey heat from the cylinder head to the cylinder block, during engine warmup, more quickly than can be accomplished by this conduction process, and the conventional above described mixing of the cooling fluid circulating within the cylinder head with the cooling fluid circulating within the cylinder block, during engine warmup, is effective for achieving this.
In the prior art, it has been proposed to provide completely independent systems for cooling the cylinder head and for cooling the cylinder block, in order to fulfil the first above described objective of cooling the cylinder head to a low temperature in order to avoid knocking, while keeping the cylinder block warmer, and each of these systems has been equipped with its own fluid pump, conduits, radiator, etc. However, such a system does not provide for the above described transfer of heat during the engine warming up process from the cylinder head to the cylinder block via the cooling fluid, and, since the cylinder block has a considerably large heat capacity, this means that the cylinder block does not warm up quickly from the cold condition, with the ill effects detailed above. Also, the provision of two independent cooling systems increases weight to an unacceptably high extent, and increases manufacturing cost. Further, since in the above described system two independent radiators are used, and the flow amount through each of them is individually regulated, it is very difficult to use total radiator cooling capacity fully, because although in some particular set of operational conditions the full cooling capacity of one radiator of one cooling system may not be completely required, it is not practicable to utilize this spare cooling capacity in order to provide additional cooling in the other cooling system, and accordingly one cooling system may become overloaded, while the other is not fully loaded. This operational inflexibility is very troublesome.